Plecoglossus altivelis
アユ

Caught these ayu (sweetfish). In Japan there is a unique way of fishing called tomo-zuri, in which one fish is hooked and lined and made to swim into another male's territory who attacks the hooked fish, hooking himself in the process.

This location caters to this type of fishing, nearby there were aquaculture raised ayu for purchase to use as live lures. In the picture you can see a difference from the natural ayu (two in the back) and the farm raised (in front), notably the spot and mouth coloration.